In many implementations, touch sensing circuits adapted for capacitive touch sensing are designed to increase the number of electrodes with respect to which sensing can be performed at the same time. Such implementations provide for enhanced resolution and high quality of touch sensing. Commonly, a mutual capacitance touch panel comprises several hundreds of sensor capacitors arrayed in a matrix having several tens of rows each including several tens of sensor capacitors. The rows of sensor capacitors are sequentially selected and sensing is performed at the same time with respect to several tens of sensor capacitors in the selected row. Therefore, the number of electrodes with respect to which sensing is performed at the same time is in the order of several tens. For a self-capacitance touch panel in which each sensor capacitor includes a sensing electrode, sensing can be performed with respect to several hundreds of sensor capacitors at the same time. Each sensor electrode simultaneously sensed with is connected to a different touch sensing circuit. This configuration may even be applied to sensor layouts where there are several hundreds of sensor capacitors similarly arrayed in a matrix having several tens of rows each including several tens of sensor capacitors. However, the number of touch sensing circuits which can be actually integrated in a practical use is restricted by the hardware scale and cost. As such, the number of electrodes with respect to which sensing can be performed at the same time is accordingly restricted.
U.S. Pat. No. 7,868,874 discloses a touch sensing circuit which provides multiplexing of sensing channels through code modulation. The touch sensing circuit is connected to a mutual capacitance touch panel which includes drive electrodes, sensing electrodes and sensor capacitors formed at respective intersections at which the drive electrodes and the sensing electrodes intersect with each other. The signals received by the sensing electrodes are multiplexed into multiple sensing channels by driving the drive electrodes with pulses modulated with codes orthogonal with each other and demodulating the signals received by the sensing electrodes with the corresponding codes. This achieves spectrum spreading of the noise and effectively improves the signal-to-noise ratio (SNR).